What is the value of using a pressure pan to test outlets? - Home Energy Pros2015-03-03T23:10:00Zhttp://homeenergypros.lbl.gov/forum/topics/what-is-the-value-of-using-a-pressure-pan-to-test-outlets?commentId=6069565%3AComment%3A92897&xg_source=activity&feed=yes&xn_auth=noIf the cavities are that tigh…tag:homeenergypros.lbl.gov,2012-09-05:6069565:Comment:930462012-09-05T17:13:40.641ZColin Gengehttp://homeenergypros.lbl.gov/profile/ColinGenge
<p>If the cavities are that tight that their pressures don't move in step with the house pressure ( or close to it) their contribution to the result or ability to affect the result in any way are microscopically small to non-existent so you don't have to worry about them either way.</p>
<p>If the cavities are that tight that their pressures don't move in step with the house pressure ( or close to it) their contribution to the result or ability to affect the result in any way are microscopically small to non-existent so you don't have to worry about them either way.</p> Michael,
That was so counter-…tag:homeenergypros.lbl.gov,2012-09-04:6069565:Comment:931032012-09-04T19:12:28.096ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>Michael,</p>
<p>That was so counter-intuitive that I had to create a spreadsheet to verify. Because standard atmospheric pressure is 101,325 Pascals (14.7 psi), a change of 50 Pa requires only a proportional change in volume of about 0.05%.</p>
<p>That would mean a hermetically-sealed 2,500 SF, 20,000 CF house would require evacuation of less than 10 CF of air to produce a pressure differential of 50 Pa.</p>
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<p>Michael,</p>
<p>That was so counter-intuitive that I had to create a spreadsheet to verify. Because standard atmospheric pressure is 101,325 Pascals (14.7 psi), a change of 50 Pa requires only a proportional change in volume of about 0.05%.</p>
<p>That would mean a hermetically-sealed 2,500 SF, 20,000 CF house would require evacuation of less than 10 CF of air to produce a pressure differential of 50 Pa.</p>
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<p></p> John-
I think I can answer t…tag:homeenergypros.lbl.gov,2012-09-04:6069565:Comment:927452012-09-04T17:56:30.971ZMichael Blasnikhttp://homeenergypros.lbl.gov/profile/MichaelBlasnik
<p>John-</p>
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<p>I think I can answer this one as well. The pressure will equalize pretty much instantly in all of the building cavities. The only exception would be for cavities that are extremely tight -- as in much less than even 1 CFM50 of leakage. </p>
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<p>The reason why pressure equalize quickly is that it takes very little flow to change the pressure in a building cavity by a lot if there is no incoming leakage to create a balance. For example, an airtight cavity 1 foot…</p>
<p>John-</p>
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<p>I think I can answer this one as well. The pressure will equalize pretty much instantly in all of the building cavities. The only exception would be for cavities that are extremely tight -- as in much less than even 1 CFM50 of leakage. </p>
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<p>The reason why pressure equalize quickly is that it takes very little flow to change the pressure in a building cavity by a lot if there is no incoming leakage to create a balance. For example, an airtight cavity 1 foot wide and 1 foot high and 15 feet long will drop in pressure by 50pa if you can remove just 1 cubic inch of air. So even a cavity that has just 1 CFM50 of leakage path to the inside and 0.1 CFM50 to the outside will take less much less than a second to reach its equilibrium pressure. </p> Hi Colin, I hope this is not…tag:homeenergypros.lbl.gov,2012-09-04:6069565:Comment:928972012-09-04T17:12:54.866ZJohn Brookshttp://homeenergypros.lbl.gov/profile/JohnBrooks
<p>Hi Colin, I hope this is not too far off topic.....</p>
<p>I found one of your Linked-In quotes about blower doors to be very fascinating.....</p>
<p>Colin Genge quote"Atmospheric pressure adjusts inside and out almost instantaneously even for a tight house. It would be in the order of a few seconds at most. The enclosure has no ability to contain pressure which is why the test fan flow leaks out as fast as it comes in."</p>
<p>I visualize that many of the building cavities of a…</p>
<p>Hi Colin, I hope this is not too far off topic.....</p>
<p>I found one of your Linked-In quotes about blower doors to be very fascinating.....</p>
<p>Colin Genge quote"Atmospheric pressure adjusts inside and out almost instantaneously even for a tight house. It would be in the order of a few seconds at most. The enclosure has no ability to contain pressure which is why the test fan flow leaks out as fast as it comes in."</p>
<p>I visualize that many of the building cavities of a house are like a 3-D network of inter-connected containers and conduits.</p>
<p>My thinking is that the building cavities(stud cavities &amp; floor cavities, etc) that are connected to the interior will behave in the same way that you described "The enclosure" above.</p>
<p>Colin, do you think that Once a blower door is cranked up ... that the atmospheric pressure inside any "connected Building Cavities" will adjust almost instantaneously?</p> Air flow is proportional, not…tag:homeenergypros.lbl.gov,2012-09-03:6069565:Comment:930012012-09-03T20:42:27.072ZRobert Riversonghttp://homeenergypros.lbl.gov/profile/RobertRiversong
<p>Air flow is proportional, not equal, to the square root of delta-P. Otherwise, you're correct.</p>
<p>Air flow is proportional, not equal, to the square root of delta-P. Otherwise, you're correct.</p> If you don't have an Exhaust…tag:homeenergypros.lbl.gov,2012-08-30:6069565:Comment:923702012-08-30T20:43:14.971ZColin Gengehttp://homeenergypros.lbl.gov/profile/ColinGenge
<p>If you don't have an Exhaust Fan Flow Meter, you could simply use a shoe box, cut a hole in it and use the formula that Paul mentioned. You can also use the "Hole Flow" feature on the DM-2 gauge to do the math for you and to calculate flow for any size of hole.</p>
<p>If you don't have an Exhaust Fan Flow Meter, you could simply use a shoe box, cut a hole in it and use the formula that Paul mentioned. You can also use the "Hole Flow" feature on the DM-2 gauge to do the math for you and to calculate flow for any size of hole.</p> David, you could use the Exha…tag:homeenergypros.lbl.gov,2012-08-30:6069565:Comment:921892012-08-30T15:11:23.201ZPaul Morinhttp://homeenergypros.lbl.gov/profile/PaulMorin
<p>David, you could use the Exhaust Fan Flow Meter to measure air flows above 10 cfm through the recessed light, but you would need to pressurize the house to 50 Pa. For flows below 10 cfm, you would need to make the hole in the Exhaust Fan Flow Meter smaller, say 3 square inches. The formula to calculate flow in CFM is 1.07 x the area of the hole in square inches x the square root of the pressure in Pa. The accuracy would be less than the stated 10% accuracy of the Flow Meter, but it would…</p>
<p>David, you could use the Exhaust Fan Flow Meter to measure air flows above 10 cfm through the recessed light, but you would need to pressurize the house to 50 Pa. For flows below 10 cfm, you would need to make the hole in the Exhaust Fan Flow Meter smaller, say 3 square inches. The formula to calculate flow in CFM is 1.07 x the area of the hole in square inches x the square root of the pressure in Pa. The accuracy would be less than the stated 10% accuracy of the Flow Meter, but it would give you a general idea.</p> Michael, I'm trying to follow…tag:homeenergypros.lbl.gov,2012-08-26:6069565:Comment:921342012-08-26T22:06:42.539ZDavid Meilandhttp://homeenergypros.lbl.gov/profile/DavidMeiland
<p>Michael, I'm trying to follow you here and wonder if you could comment on the following example. We recently did work on a house with a large number of can lights, some with floor above and others with open attic above. Lots of pressure pan readings in the 40pa range at these lights, with the house at -50. I can't tell from your description whether these pressures can be turned into any sort of CFM50 number. It sounds like you're saying no to that.</p>
<p>There is of course a lot of…</p>
<p>Michael, I'm trying to follow you here and wonder if you could comment on the following example. We recently did work on a house with a large number of can lights, some with floor above and others with open attic above. Lots of pressure pan readings in the 40pa range at these lights, with the house at -50. I can't tell from your description whether these pressures can be turned into any sort of CFM50 number. It sounds like you're saying no to that.</p>
<p>There is of course a lot of perceptible air leakage, especially around the hole cut in the drywall. We are easily able to seal these down into the 10-15pa range. This seems to translate into a reduction of maybe 2 CFM50 per can, based on very crude analysis. As stated above I don't have a tool for measuring this. </p> Colin-
I just have to chime…tag:homeenergypros.lbl.gov,2012-08-26:6069565:Comment:921302012-08-26T20:18:49.994ZMichael Blasnikhttp://homeenergypros.lbl.gov/profile/MichaelBlasnik
Colin-<br></br>
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I just have to chime in here - the dP across the pressure pan has nothing to do with how leaky the outlet is. When covered by the pressure pan the outlet leak has no flow - it has become a pressure tap into the wall cavity. The pressure is related to the ratio of the size of leakage paths to the inside vs. outside, excluding the outlet. Also, I would not estimate this ratio as 7 ( the square root of the ratio of the dPs) but as closer to 12 (49^0.65=12.5) since 0.65 is a more…
Colin-<br/>
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I just have to chime in here - the dP across the pressure pan has nothing to do with how leaky the outlet is. When covered by the pressure pan the outlet leak has no flow - it has become a pressure tap into the wall cavity. The pressure is related to the ratio of the size of leakage paths to the inside vs. outside, excluding the outlet. Also, I would not estimate this ratio as 7 ( the square root of the ratio of the dPs) but as closer to 12 (49^0.65=12.5) since 0.65 is a more typical flow exponent for building leaks. I would also not take this number too literally given how sensitive it would be to small measurement errors. I've thought of doing that. I…tag:homeenergypros.lbl.gov,2012-08-26:6069565:Comment:921282012-08-26T14:29:23.338ZDavid Meilandhttp://homeenergypros.lbl.gov/profile/DavidMeiland
<p>I've thought of doing that. I have a building that's perfect for it, and I actually already have a very large supply of the gaskets, which were given to me . However, what I've observed it that air comes right through the receptacle or switch itself, so my guess is that I could only shave a few CFM50 off the entire building by installing the gaskets, not enough to pay back. I've done enough air sealing to know that you want to find larger holes than that, hopefully some massive…</p>
<p>I've thought of doing that. I have a building that's perfect for it, and I actually already have a very large supply of the gaskets, which were given to me . However, what I've observed it that air comes right through the receptacle or switch itself, so my guess is that I could only shave a few CFM50 off the entire building by installing the gaskets, not enough to pay back. I've done enough air sealing to know that you want to find larger holes than that, hopefully some massive ones.</p>
<p>In spite of this, I remodeled my house this year and installed those damn things at every hole, thinking "what if they make a difference??" and besides, I still have hundreds left.</p>
<p>I don't have a flow hood, but it would be interesting to have one long enough to do some testing on various common holes. We do use the pressure pan on can lights and other common holes sometimes.</p>